<?xml version="1.0" encoding="utf-8"?>
 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
    <head>
        <meta charset="utf-8" />
        <title>EPUB 3 Overview</title>
        <link rel="stylesheet" type="text/css" href="../css/epub-spec.css" />
    </head>
    <body>
        <h1 class="title">EPUB 3 Overview</h1>
        <p class="identity"><span class="releaseinfo">Recommended Specification</span>
            <span class="pubdate">11 October 2011</span></p>
        <dl class="printhistory">
            <dt>This version</dt>
            <dd><a href="http://www.idpf.org/epub/30/spec/epub30-overview-20111011.html"
                    >http://www.idpf.org/epub/30/spec/epub30-overview-20111011.html</a></dd>
            <dt>Latest version</dt>
            <dd><a href="http://www.idpf.org/epub/30/spec/epub30-overview.html"
                    >http://www.idpf.org/epub/30/spec/epub30-overview.html</a></dd>
            <dt>Previous version</dt>
            <dd><a href="http://www.idpf.org/epub/30/spec/epub30-overview-20110908.html"
                    >http://www.idpf.org/epub/30/spec/epub30-overview-20110908.html</a></dd>
        </dl>
        <p class="diff"> A diff of changes from the previous draft is available at <a
                href="http://code.google.com/p/epub-revision/source/diff?spec=svn3218&amp;old=3183&amp;r=3218&amp;format=side&amp;path=%2Ftrunk%2Fsrc%2Fspec%2Fepub30-overview.xml"
                >this link</a>. </p>
        <div class="legal"><p class="copyright">Copyright © 2010, 2011 International Digital
                Publishing Forum™</p><div class="legalnotice" title="Legal Notice"><a id="d66911e37"
                    ></a><p>All rights reserved. This work is protected under Title 17 of the United
                    States Code. Reproduction and dissemination of this work with changes is
                    prohibited except with the written permission of the <a
                        href="http://www.idpf.org">International Digital Publishing Forum
                    (IDPF)</a>. </p><p>EPUB is a registered trademark of the International Digital
                    Publishing Forum.</p></div></div>
        <div class="authorgroup"><p class="bridgehead">Editors</p><p class="editor">Garth Conboy,
                Google Inc. </p><p class="editor">Matt Garrish, Invited Expert </p><p class="editor"
                >Markus Gylling, DAISY Consortium </p><p class="editor">William McCoy, International
                Digital Publishing Forum (IDPF) </p><p class="editor">MURATA Makoto, JEPA EPUB Study
                Group </p><p class="editor">Daniel Weck, DAISY Consortium </p></div>
        <nav class="toc" id="toc">
            <p><strong>Table of Contents</strong></p>
            <ol>
                <!-- broken frag ref: -->
                <li><a href="#sec-intro-error">1. Introduction</a></li>
                <li><ol>
                        <li><a href="#sec-intro-overview">1.1. Overview</a></li>
                        <li><a href="#sec-intro-roadmap">1.2. Roadmap</a></li>
                    </ol></li>
                <li><a href="#sec-features">2. Features</a></li>
                <li><ol>
                        <li><a href="#sec-package-file">2.1. Package Document</a></li>
                        <li><a href="#sec-nav">2.2. Navigation</a></li>
                        <li><ol>
                                <li><a href="#sec-nav-order">2.2.1. Reading Order</a></li>
                                <li><a href="#sec-nav-nav-doc">2.2.2. Navigation Document</a></li>
                            </ol></li>
                        <li><a href="#sec-linking">2.3. Linking</a></li>
                        <li><a href="#sec-metadata">2.4. Metadata</a></li>
                        <li><a href="#sec-content-docs">2.5. Content Documents</a></li>
                        <li><a href="#sec-rendering">2.6. Rendering and CSS</a></li>
                        <li><a href="#sec-multimedia">2.7. Multimedia</a></li>
                        <li><a href="#sec-fonts">2.8. Fonts</a></li>
                        <li><a href="#sec-scripting">2.9. Scripting</a></li>
                        <li><a href="#sec-tts">2.10. Text-to-speech</a></li>
                        <li><a href="#sec-container">2.11. Container</a></li>
                    </ol></li>
                <li><a href="#sec-gls">3. Global Language Support</a></li>
                <li><ol>
                        <li><a href="#sec-gls-metadata">3.1. Metadata</a></li>
                        <li><a href="#sec-gls-content-docs">3.2. Content Documents</a></li>
                        <li><a href="#sec-gls-css">3.3. CSS</a></li>
                        <li><a href="#sec-gls-fonts">3.4. Fonts</a></li>
                        <li><a href="#sec-gls-tts">3.5. Text-to-speech</a></li>
                        <li><a href="#sec-gls-container">3.6. Container</a></li>
                    </ol></li>
                <li><a href="#sec-accessibility">4. Accessibility</a></li>
                <li><ol>
                        <li><a href="#sec-access-nav">4.1. Navigation</a></li>
                        <li><a href="#sec-access-semantic-markup">4.2. Semantic Markup</a></li>
                        <li><a href="#sec-access-layout">4.3. Dynamic Layouts</a></li>
                        <li><a href="#sec-access-overlays">4.4. Aural Renditions and Media
                                Overlays</a></li>
                        <li><a href="#sec-access-fallbacks">4.5. Fallbacks</a></li>
                        <li><a href="#sec-access-scripting">4.6. Scripting</a></li>
                    </ol></li>
                <li><ol></ol></li>
            </ol>
        </nav>
        <section class="chapter" title="1 Introduction" id="sec-intro">
            <h2 class="title"><span class="link-marker"><a class="hidden-reveal" title="Link here"
                        href="#sec-intro">›</a> </span>1 Introduction</h2>
            <section class="section" title="1.1 Overview" id="sec-intro-overview">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-intro-overview">›</a> </span>1.1
                    Overview</h3>
                <p>The EPUB® specification is a distribution and interchange format standard for
                    digital publications and documents. EPUB defines a means of representing,
                    packaging and encoding structured and semantically enhanced Web content —
                    including HTML5, CSS, SVG, images, and other resources — for distribution in a
                    single-file format.</p>
                <p id="sibling-specs">EPUB 3, the third major release of the standard, consists of a
                    set of four specifications, each defining an important component of an overall
                    <!-- broken cross-doc frag ref: -->
                        <a class="glossterm" href="epub30-terminology.xhtml#error-gloss-epub-publication"
                        title="EPUB Publication (or Publication)">EPUB Publication</a>:</p>
                <div class="itemizedlist" id="epub-specs-listing"><ul class="itemizedlist">
                        <li class="listitem"><p>EPUB Publications 3.0 <a class="biblioref"
                                    href="epub30-references.xhtml#refPublications3"
                                    title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a>,
                                which defines publication-level semantics and overarching
                                conformance requirements for <a class="glossterm"
                                    href="epub30-terminology.xhtml#gloss-epub-publication"
                                    title="EPUB Publication (or Publication)">EPUB
                                Publication</a>s.</p></li>
                        <li class="listitem"><p>EPUB Content Documents 3.0 <a class="biblioref"
                                    href="epub30-references.xhtml#refContentDocs3"
                                    title="EPUB Content Documents 3.0"
                                    >[<abbr>ContentDocs30</abbr>]</a>, which defines profiles of
                                XHTML, SVG and CSS for use in the context of <a class="glossterm"
                                    href="epub30-terminology.xhtml#gloss-epub-publication"
                                    title="EPUB Publication (or Publication)">EPUB
                                Publication</a>s.</p></li>
                        <li class="listitem"><p>EPUB Open Container Format (OCF) 3.0 <a
                                    class="biblioref" href="epub30-references.xhtml#refOCF30"
                                    title="Open Container Format 3.0">[<abbr>OCF3</abbr>]</a>, which
                                defines a file format and processing model for encapsulating a set
                                of related resources into a single-file (ZIP) <a class="glossterm"
                                    href="epub30-terminology.xhtml#gloss-container"
                                    title="EPUB Container (or Container)">EPUB Container</a>.
                            </p></li>
                        <li class="listitem"><p>EPUB Media Overlays 3.0 <a class="biblioref"
                                    href="epub30-references.xhtml#refOverlays3"
                                    title="EPUB Media Overlays 3.0"
                                    >[<abbr>MediaOverlays30</abbr>]</a>, which defines a format and
                                a processing model for synchronization of text and audio.</p></li>
                    </ul></div>
                <p>EPUB has been widely adopted as the format for digital books (eBooks), and these
                    new specifications significantly increase the format's capabilities in order to
                    better support a wider range of publication requirements, including complex
                    layouts, rich media and interactivity, and global typography features. The
                    expectation is that EPUB 3 will be utilized for a broad range of content,
                    including books, magazines and educational, professional and scientific
                    publications.</p>
                <p>This document provides a starting point for content authors and software
                    developers wishing to understand these specifications. It consists of
                    non-normative overview material, including a <a href="#sec-intro-roadmap"
                        title="1.2 Roadmap">roadmap</a> to the four building-block specification
                    documents that compose EPUB 3.</p>
                <p>Another non-normative document, EPUB 3 Changes from EPUB 2.0.1 <a
                        class="biblioref" href="epub30-references.xhtml#refEPUB3Changes"
                        title="EPUB 3 Differences from EPUB 2.0.1">[<abbr>EPUB3Changes</abbr>]</a>,
                    describes changes in EPUB 3 from the previous version, but is intended primarily
                    for <a class="glossterm" href="epub30-terminology.xhtml#gloss-author"
                        title="Author">Author</a>s and <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-epub-reading-system"
                        title="EPUB Reading System (or Reading System)">EPUB Reading System</a>
                    vendors migrating from EPUB 2.0.1 to EPUB 3 and for those who anticipate
                    supporting both versions.</p>
            </section>
            <section class="section" title="1.2 Roadmap" id="sec-intro-roadmap">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-intro-roadmap">›</a> </span>1.2
                    Roadmap</h3>
                <p>This section provides an overview of the EPUB 3 specifications by explaining in
                    brief the components of a Publication. Links to additional information within
                    this document and to the specifications are included.</p>
                <p>An <a class="glossterm" href="epub30-terminology.xhtml#gloss-epub-publication"
                        title="EPUB Publication (or Publication)">EPUB Publication</a>, at its most
                    basic level, is a bundled collection of resources that can be reliably and
                    predictably ingested by an <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-epub-reading-system"
                        title="EPUB Reading System (or Reading System)">EPUB Reading System</a> in
                    order to render its contents to a <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-user" title="User">User</a>. Some of
                    these resources facilitate the discovery and processing of the EPUB Publication,
                    while others make up the content of the source publication. The latter, <a
                        class="glossterm"
                        href="epub30-terminology.xhtml#gloss-content-document-epub"
                        title="EPUB Content Document">EPUB Content Document</a>s, are described in
                        <a class="xref" href="#sec-content-docs" title="2.5 Content Documents"
                        >Content Documents</a> and are fully defined in <a class="biblioref"
                        href="epub30-references.xhtml#refContentDocs3"
                        title="EPUB Content Documents 3.0">[<abbr>ContentDocs30</abbr>]</a>. </p>
                <p>A Publication's resources are typically bundled for distribution as a ZIP-based
                    archive with the file extension <code class="literal">.epub</code>. As
                    conformant ZIP archives, Publications can be unzipped by many software programs,
                    simplifying both their production and consumption. The container format is
                    introduced in <a class="xref" href="#sec-container" title="2.11 Container"
                        >Container</a> and defined in <a class="biblioref"
                        href="epub30-references.xhtml#refOCF30" title="Open Container Format 3.0"
                            >[<abbr>OCF3</abbr>]</a>. </p>
                <p>The container format not only provides a means of determining that the zipped
                    content represents an EPUB Publication (the <code class="filename"
                        >mimetype</code> file), but also provides a universally-named directory of
                    informative resources (<code class="filename">/META-INF</code>). Key among these
                    is the <code class="filename">container.xml</code> file, which directs Reading
                    Systems to the root file of the Publication, the <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-package-document"
                        title="Package Document">Package Document</a>. </p>
                <p>The Package Document is itself a kind of information warehouse for the
                    Publication, storing metadata about the specific work contained in the
                    Publication, providing an exhaustive list of resources and defining a default
                    reading order. The Package Document is introduced in <a class="xref"
                        href="#sec-package-file" title="2.1 Package Document">Package Document</a>
                    and defined in <a class="biblioref"
                        href="epub30-references.xhtml#refPublications3"
                        title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a>. </p>
                <p>The preceding components of an EPUB Publication are not new to EPUB 3, and will
                    be familiar to anyone who has worked with Publications before, although they
                    have been changed and enhanced in this version. A new core addition to EPUB 3,
                    however, is the <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-media-overlay-document"
                        title="Media Overlay Document">Media Overlay Document</a>, which defines a
                    means of synchronizing text and audio playback. The Overlay Document is
                    introduced in <a class="xref" href="#sec-multimedia" title="2.7 Multimedia"
                        >Multimedia</a> and defined in <a class="biblioref"
                        href="epub30-references.xhtml#refOverlays3" title="EPUB Media Overlays 3.0"
                            >[<abbr>MediaOverlays30</abbr>]</a>. </p>
                <p>The following example shows the resources a minimal "Hello World" Publication
                    might contain:</p>
                <div class="informalexample"
                    ><pre class="synopsis">
mimetype
META-INF/container.xml
Content/HelloWorld.opf
Content/HelloWorld.xhtml
</pre></div>
                <p>While conceptually simple, an EPUB Publication is more than just a collection of
                    HTML pages and dependent assets in a ZIP package as represented in this example.
                    The following sections of this document delve into more detail about the primary
                    features and functionality that Publications provide to enhance the reading
                    experience.</p>
            </section>
        </section>
        <section class="chapter" title="2 Features" id="sec-features">
            <h2 class="title"><span class="link-marker"><a class="hidden-reveal" title="Link here"
                        href="#sec-features">›</a> </span>2 Features</h2>
            <p>This section covers the major features of EPUB, including important components and
                topics that apply to the process of authoring <a class="glossterm"
                    href="epub30-terminology.xhtml#gloss-epub-publication"
                    title="EPUB Publication (or Publication)">EPUB Publication</a>s as a whole.</p>
            <section class="section" title="2.1 Package Document" id="sec-package-file">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-package-file">›</a> </span>2.1 Package
                    Document</h3>
                <p>Every EPUB Publication includes a single <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-package-document"
                        title="Package Document">Package Document</a>, which specifies all the
                    Publication's constituent content documents and their required resources,
                    defines a reading order for linear consumption, and associates Publication-level
                    metadata and navigation information.</p>
                <p>The Package Document represents a significant improvement on a typical Web site.
                    A Web site, for example, embeds references to its resources within its content,
                    which, while a simple and flexible means of identifying resources, makes it
                    difficult to enumerate all the resources required to render it. In addition,
                    there is no standard way for a Web site to define that a sequence of pages make
                    up a larger publication, which is precisely what EPUB's <code>spine</code>
                    element does (i.e., it provides an external declarative means to explicitly
                    specify navigation through a collection of documents). Finally, the Package
                    Document defines a standard way to represent metadata globally applicable to a
                    collection of pages.</p>
                <p>The Package Document and other Publication-level constructs are specified in <a
                        class="biblioref" href="epub30-references.xhtml#refPublications3"
                        title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a>. </p>
            </section>
            <section class="section" title="2.2 Navigation" id="sec-nav">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-nav">›</a> </span>2.2 Navigation</h3>
                <section class="section" title="2.2.1 Reading Order" id="sec-nav-order">
                    <h4 class="title"><span class="link-marker"><a class="hidden-reveal"
                                title="Link here" href="#sec-nav-order">›</a> </span>2.2.1 Reading
                        Order</h4>
                    <p>A key concept of EPUB is that a Publication consists of multiple resources
                        that may be completely navigated and consumed by a person or program <span
                            class="italic">in some specific order</span>.</p>
                    <p>Many publications have an obvious reading order, or logical progression
                        through their content. A novel is an example of a highly sequential document
                        — it typically has a beginning, middle and end — but not all publications
                        are so ordered: a cookbook or collection of photographic images might be
                        considered to be more like a database. All documents do, however, have at
                        least one logical ordering of all their top-level content items, whether by
                        date, topic, location or some other criteria (e.g., a cookbook is typically
                        ordered by type of recipe).</p>
                    <p>Every EPUB Publication defines at least one such logical ordering of all its
                        top-level content (the <span class="phrase"><a
                                href="epub30-publications.xhtml#sec-spine-elem">spine</a>
                            <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                                title="EPUB Publications 3.0"
                            >[<abbr>Publications30</abbr>]</a></span>), as well as a declarative
                        table of contents (the <a class="glossterm"
                            href="epub30-terminology.xhtml#gloss-content-document-epub-nav"
                            title="EPUB Navigation Document">EPUB Navigation Document</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0">[<abbr>ContentDocs30</abbr>]</a>).
                        Publications make these data structures available in a machine-readable way
                            <span class="italic">external</span> to the content, simplifying their
                        discovery and use.</p>
                    <p>EPUB Publications are not limited to the linear ordering of their contents,
                        nor do they preclude linking in arbitrary ways — just like the Web, EPUB
                        Publications are built on hypertext — but the basic consumption and
                        navigation can be reliably accomplished in a way that is not true for a set
                        of HTML pages.</p>
                </section>
                <section class="section" title="2.2.2 Navigation Document" id="sec-nav-nav-doc">
                    <h4 class="title"><span class="link-marker"><a class="hidden-reveal"
                                title="Link here" href="#sec-nav-nav-doc">›</a> </span>2.2.2
                        Navigation Document</h4>
                    <p>Every EPUB Publication contains a special XHTML Content Document called the
                            <a class="glossterm"
                            href="epub30-terminology.xhtml#gloss-content-document-epub-nav"
                            title="EPUB Navigation Document">EPUB Navigation Document</a>, which
                        uses the HTML5 <code>nav</code> element to define human- and
                        machine-readable navigation information.</p>
                    <p>The Navigation Document supersedes the NCX document <a class="biblioref"
                            href="epub30-references.xhtml#refOPS2"
                            title="Open Publication Structure 2.0.1">[<abbr>OPS2</abbr>]</a>, and
                        the inclusion of NCX documents is only recommended for forward compatibility
                        in older Reading Systems. The Navigation Document, while maintaining the
                        baseline accessibility and navigation support and features of the NCX,
                        introduces new functionality and rendering features to enhance navigation
                        for all Users. Prime among these are better support for internationalization
                        (as an XHTML5 document itself, the Navigation Document natively supports
                        ruby annotations) and support for embedded grammars (MathML and SVG can be
                        included within navigation links).</p>
                    <p>As XHTML Content Documents, Navigation Documents also provide a flexible
                        means of tailoring the navigation display using CSS and the <span
                            class="phrase"><a
                                href="epub30-contentdocs.xhtml#sec-xhtml-nav-def-hidden">hidden
                                attribute</a>
                            <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                                title="EPUB Content Documents 3.0"
                            >[<abbr>ContentDocs30</abbr>]</a></span> while not impacting access to
                        information for accessible Reading Systems.</p>
                    <p>The structure and semantics of Navigation Documents are defined in <span
                            class="phrase"><a href="epub30-contentdocs.xhtml#sec-xhtml-nav">EPUB
                                Navigation Documents</a>
                            <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                                title="EPUB Content Documents 3.0"
                            >[<abbr>ContentDocs30</abbr>]</a></span>.</p>
                </section>
            </section>
            <section class="section" title="2.3 Linking" id="sec-linking">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-linking">›</a> </span>2.3 Linking</h3>
                <p>The new EPUB Canonical Fragment Identifier (epubcfi) Specification <a
                        class="biblioref" href="epub30-references.xhtml#refEPUBCFI"
                        title="EPUB Canonical Fragment Identifier (epubcfi) Specification"
                            >[<abbr>EPUBCFI</abbr>]</a> defines a standardized method for linking
                    into a Publication. </p>
                <p>Required support for this scheme in Reading Systems means that EPUB now has an
                    interoperable linking mechanism, one that can, for example, facilitate the
                    sharing of bookmarks and reading locations across devices.</p>
            </section>
            <section class="section" title="2.4 Metadata" id="sec-metadata">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-metadata">›</a> </span>2.4 Metadata</h3>
                <p>EPUB Publications provide a rich array of options for adding Publication
                    metadata. The Package Document includes a dedicated <span class="phrase"><a
                            href="epub30-publications.xhtml#sec-metadata-elem">metadata section</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>
                    for general information about the Publication, allowing titles, authors,
                    identifiers and other information about the Publication to be easily accessed.
                    It also provides the means to attach complete bibliographic records to a
                    Publication using the <span class="phrase"><a
                            href="epub30-publications.xhtml#sec-link-elem">link element</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0"
                    >[<abbr>Publications30</abbr>]</a></span>.</p>
                <p>The Package Document also allows a <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-unique-identifier"
                        title="Unique Identifier">Unique Identifier</a> to be established for a
                    Publication using the <span class="phrase"><a
                            href="epub30-publications.xhtml#attrdef-package-unique-identifier"
                            >unique-identifier attribute</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>.
                    The required last-modified date in the Package metadata section can be joined
                    with this identifier to define a <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-package-identifier"
                        title="Package Identifier">Package Identifier</a>, which provides a means of
                    distinguishing EPUB Publications that represent different versions of the same
                        <a class="glossterm" href="epub30-terminology.xhtml#gloss-manifestation"
                        title="Manifestation">Manifestation</a> (see <span class="phrase"><a
                            href="epub30-publications.xhtml#sec-package-metadata-identifiers"
                            >Publication Identifiers</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>).
                    The Package Identifier addresses the issue of how to release a Publication
                    without changing its Unique Identifier while still identifying it as a new
                    version.</p>
                <p>XHTML Content Documents also include the means of annotating document markup with
                    rich metadata, making them more semantically meaningful and useful both for
                    processing and accessibility purposes (<span class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-xhtml-semantic-inflection">Semantic
                            Inflection</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span>).</p>
            </section>
            <section class="section" title="2.5 Content Documents" id="sec-content-docs">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-content-docs">›</a> </span>2.5 Content
                    Documents</h3>
                <p>Every EPUB Publication contains one or more <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-content-document-epub"
                        title="EPUB Content Document">EPUB Content Document</a>s, as defined in <a
                        class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                        title="EPUB Content Documents 3.0">[<abbr>ContentDocs30</abbr>]</a>. These
                    are XHTML or SVG documents that describe the readable content of a Publication
                    and reference associated media resources (e.g., images, audio and video
                    clips).</p>
                <p><a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-content-document-epub-xhtml"
                        title="XHTML Content Document">XHTML Content Document</a>s are defined by a
                    profile of HTML5 that requires the use of XML serialization <a class="biblioref"
                        href="epub30-references.xhtml#refHTML5"
                        title="HTML5: A vocabulary and associated APIs for HTML and XHTML"
                            >[<abbr>HTML5</abbr>]</a> in order to ensure that content can be
                    reliably manipulated and rendered. This profile also adds two additional
                    EPUB-specific language constructs: the <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#attrdef-epub-type">epub:type
                            attribute</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> for element-level metadata and the
                        <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-xhtml-epub-trigger">epub:trigger
                            element</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> for declaratively associating
                    controls with multimedia elements.</p>
                <p>These additions do not affect the ability of an HTML5 User Agent <a
                        class="biblioref" href="epub30-references.xhtml#refHTML5"
                        title="HTML5: A vocabulary and associated APIs for HTML and XHTML"
                            >[<abbr>HTML5</abbr>]</a> to render EPUB XHTML Content Documents, but
                    Publications might not render identically in all User Agents depending on their
                    support.</p>
            </section>
            <section class="section" title="2.6 Rendering and CSS" id="sec-rendering">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-rendering">›</a> </span>2.6 Rendering and
                    CSS</h3>
                <p>A key concept of EPUB is that content presentation should adapt to the User
                    rather than the User having to adapt to a particular presentation of content.
                    HTML was originally designed to support dynamic rendering of structured content,
                    but over time HTML as supported in Web browsers has become focused on the needs
                    of Web applications, and most popular Web sites now have fixed-format
                    layouts.</p>
                <p>EPUB Publications, however, are designed to maximize accessibility for the
                    visually impaired, and Reading Systems typically perform text line layout and
                    pagination on the fly, adapting to the size of the display area, the User's
                    preferred font size, and other environmental factors. This behavior is not
                    guaranteed in EPUB; images, vector graphics, video and other non-reflowable
                    content may be included, and some Reading Systems might not paginate on the fly,
                    or at all. Nevertheless, supporting dynamic adaptive layout and accessibility
                    has been a primary design consideration throughout the evolution of the EPUB
                    standard.</p>
                <p>EPUB Content Documents may optionally reference <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-stylesheet"
                        title="EPUB Style Sheet (or Style Sheet)">EPUB Style Sheet</a>s, allowing
                    Authors to define the desired rendering properties. EPUB 3 defines a profile of
                    CSS based on CSS 2.1 <a class="biblioref"
                        href="epub30-references.xhtml#refCSS21"
                        title="Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification"
                            >[<abbr>CSS2.1</abbr>]</a> for this purpose, together with capabilities
                    defined by various CSS3 Modules and several additional properties specific to
                    EPUB.</p>
                <p>CSS3 properties were selected based on their current level of support in Web
                    browsers, but support for them in Reading Systems and User Agents is not
                    guaranteed (EPUB-defined properties may similarly be ignored).</p>
                <p>EPUB 3 also supports CSS styles that enable both horizontal and vertical layout
                    and both left-to-right and right-to-left writing, but Reading Systems might not
                    support all of these capabilities. Reading Systems may also support different
                    rendering options than the Author intended. Refer to <a class="xref"
                        href="#sec-gls-css" title="3.3 CSS">CSS</a> in the Global Language Support
                    section for more information.</p>
                <p>EPUB 3 also supports the ability to include multiple style sheets that allow
                    users, for example, to select between day/night reading modes or to change the
                    rendering direction of the text. Refer to <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-xhtml-alternate-style-tags">Alternate
                            Style Tags</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> for more information.</p>
            </section>
            <section class="section" title="2.7 Multimedia" id="sec-multimedia">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-multimedia">›</a> </span>2.7
                    Multimedia</h3>
                <p>EPUB 3 supports audio and video embedded in [content documents] via the new <a
                        class="biblioref" href="epub30-references.xhtml#refHTML5"
                        title="HTML5: A vocabulary and associated APIs for HTML and XHTML"
                            >[<abbr>HTML5</abbr>]</a>
                    <code>audio</code> and <code>video</code> elements, inheriting all the
                    functionality and features these elements provide. (For information on supported
                    audio formats, please refer to <span class="phrase"><a
                            href="epub30-publications.xhtml#sec-core-media-types">Core Media
                            Types</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>.
                    For recommendations on embedding video, refer to <span class="phrase"><a
                            href="epub30-publications.xhtml#note-video-codecs">Reading System
                            Conformance</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0"
                    >[<abbr>Publications30</abbr>]</a></span>.)</p>
                <p>Another key new multimedia feature in EPUB 3 is the inclusion of <a
                        class="glossterm"
                        href="epub30-terminology.xhtml#gloss-media-overlay-document"
                        title="Media Overlay Document">Media Overlay Document</a>s <a
                        class="biblioref" href="epub30-references.xhtml#refOverlays3"
                        title="EPUB Media Overlays 3.0">[<abbr>MediaOverlays30</abbr>]</a>. When
                    pre-recorded narration is available for a Publication, Media Overlays provide
                    the ability to synchronize that audio with the text of a Content Document (see
                    also <a class="xref" href="#sec-access-overlays"
                        title="4.4 Aural Renditions and Media Overlays">Aural Renditions and Media
                        Overlays</a>).</p>
            </section>
            <section class="section" title="2.8 Fonts" id="sec-fonts">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-fonts">›</a> </span>2.8 Fonts</h3>
                <p>EPUB 3 supports two closely-related font formats — OpenType <a class="biblioref"
                        href="epub30-references.xhtml#refOpenType"
                        title="ISO/IEC 14496-22:2009 - Information technology -- Coding of audio-visual objects -- Part 22: Open Font Format"
                            >[<abbr>OpenType</abbr>]</a> and WOFF <a class="biblioref"
                        href="epub30-references.xhtml#refWOFF" title="WOFF File Format 1.0"
                            >[<abbr>WOFF</abbr>]</a> — to accommodate both traditional publishing
                    workflows and emerging Web-based workflows. Word processing programs used to
                    create Publications are likely to have access only to a collection of installed
                    OpenType fonts, for example, whereas Web-archival EPUB generators will likely
                    only have access to WOFF resources (which cannot be converted to OpenType
                    without undesirable, and potentially unlicensed, stripping of WOFF
                    metadata).</p>
                <p>EPUB 3 also supports both obfuscated and regular font resources for both OpenType
                    and WOFF font formats. Support for obfuscated font resources is required to
                    accommodate font licensing restrictions for many commercially-available
                    fonts.</p>
            </section>
            <section class="section" title="2.9 Scripting" id="sec-scripting">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-scripting">›</a> </span>2.9 Scripting</h3>
                <p>EPUB strives to treat content <span class="italic">declaratively</span> — as data
                    that can be manipulated, not programs that must be executed — but does support
                    scripting as defined in <a class="biblioref"
                        href="epub30-references.xhtml#refHTML5"
                        title="HTML5: A vocabulary and associated APIs for HTML and XHTML">HTML5</a>
                    and <a class="biblioref" href="epub30-references.xhtml#refSVG"
                        title="Scalable Vector Graphics (SVG) 1.1 (Second Edition)">SVG</a> (refer
                    to <span class="phrase"><a href="epub30-contentdocs.xhtml#sec-scripted-content"
                            >Scripted Content Documents</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> for more information).</p>
                <p>It is important to note, however, that scripting support is optional for Reading
                    Systems and may be disabled for security reasons. </p>
                <p>Authors should also note that scripting in an EPUB Publication can create
                    security considerations that are different from scripting within a Web browser.
                    For example, typical same-origin policies are not applicable to content that has
                    been downloaded to a User's local system. Therefore, it is strongly encouraged
                    that scripting be limited to container constrained contexts, as further
                    described in <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-scripted-content-content-reqs"
                            >Scripted Content Documents — Content Conformance</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span>.</p>
                <p>Scripting consequently should be used only when essential to the User experience,
                    since it greatly increases the likelihood that content will not be portable
                    across all Reading Systems and creates barriers to accessibility and content
                    reusability.</p>
            </section>
            <section class="section" title="2.10 Text-to-speech" id="sec-tts">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-tts">›</a> </span>2.10 Text-to-speech</h3>
                <p>EPUB 3 provides the following text-to-speech (TTS) facilities for controlling
                    aspects of speech synthesis, such as pronunciation, prosody and voice
                    characteristics:</p>
                <div class="variablelist"><dl>
                        <dt class="varlistentry"><span class="term"><code>Pronunciation
                                    Lexicons</code></span></dt>
                        <dd><p>The inclusion of generic pronunciation lexicons using the W3C PLS
                                format <a class="biblioref" href="epub30-references.xhtml#refPLS"
                                    title="Pronunciation Lexicon Specification 1.0 (PLS)"
                                        >[<abbr>PLS</abbr>]</a> enables Authors to provide
                                pronunciation rules that apply to the entire EPUB Publication. Refer
                                to <span class="phrase"><a href="epub30-contentdocs.xhtml#sec-pls"
                                        >PLS Documents</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> for more
                                information. </p></dd>
                        <dt class="varlistentry"><span class="term"><code>Inline SSML
                                    Phonemes</code></span></dt>
                        <dd><p> The incorporation of SSML phonemes functionality <a
                                    class="biblioref" href="epub30-references.xhtml#refSSML"
                                    title="Speech Synthesis Markup Language (SSML) Version 1.1"
                                        >[<abbr>SSML</abbr>]</a> directly into a <span
                                    class="phrase"><a
                                        href="epub30-terminology.xhtml#gloss-content-document-epub"
                                        >EPUB Content Document</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> enables
                                fine-grained pronunciation control, taking precedence over default
                                pronunciation rules and/or referenced pronunciation lexicons (as
                                provided by the PLS format mentioned above). Refer to <span
                                    class="phrase"><a
                                        href="epub30-contentdocs.xhtml#sec-xhtml-ssml-attrib">SSML
                                        Attributes</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> for more
                                information. </p></dd>
                        <dt class="varlistentry"><span class="term"><code>CSS Speech
                                Features</code></span></dt>
                        <dd><p> The inclusion of a select set of features from the CSS 3 Speech
                                Module <a class="biblioref"
                                    href="epub30-references.xhtml#refCSS3Speech"
                                    title="CSS3 Speech Module">[<abbr>CSS3Speech</abbr>]</a>
                                (previously known as CSS 2.1 Aural Stylesheets <a class="biblioref"
                                    href="epub30-references.xhtml#refCSS21"
                                    title="Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification"
                                        >[<abbr>CSS2.1</abbr>]</a>) enables Authors to control
                                further speech synthesis characteristics. Refer to <span
                                    class="phrase"><a
                                        href="epub30-contentdocs.xhtml#sec-css-voice-characteristics"
                                        >CSS 3.0 Speech</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> for more
                                information.</p></dd>
                    </dl></div>
            </section>
            <section class="section" title="2.11 Container" id="sec-container">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-container">›</a> </span>2.11 Container</h3>
                <p>An EPUB Publication is transported and interchanged as a single file (a "portable
                    document") that contains the Package Document, all Content Documents and all
                    other required resources for processing the Publication. The single-file
                    container format for EPUB is based on the widely adopted ZIP format. An XML
                    manifest that specifies the location in the ZIP archive of the Package Document
                    must be found at a well-defined location within the archive.</p>
                <p>This approach provides a clear contract between any creator of an EPUB
                    Publication and any system which consumes such Publications, as well as a
                    reliable representation that is independent of network transport or file system
                    specifics.</p>
                <p>An EPUB Publication's representation as a container file is specified in <a
                        class="biblioref" href="epub30-references.xhtml#refOCF30"
                        title="Open Container Format 3.0">[<abbr>OCF3</abbr>]</a>. </p>
            </section>
        </section>
        <section class="chapter" title="3 Global Language Support" id="sec-gls">
            <h2 class="title"><span class="link-marker"><a class="hidden-reveal" title="Link here"
                        href="#sec-gls">›</a> </span>3 Global Language Support</h2>
            <section class="section" title="3.1 Metadata" id="sec-gls-metadata">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-gls-metadata">›</a> </span>3.1
                    Metadata</h3>
                <p>EPUB 3 supports alternate representations of all text metadata items in the
                    package metadata section to improve global distribution of Publications. The
                        <code class="literal">alternate-script</code> property can be combined with
                    the <code>xml:lang</code> attribute to include and identify alternate script
                    renditions of language-specific metadata.</p>
                <p>Using this property, a Japanese Publication could, for example, include an
                    alternate Roman-script representation of the author's name and/or one or more
                    representations of the title in Romance languages. Refer to the <span
                        class="phrase"><a href="epub30-publications.xhtml#alternate-script"
                            >alternate-script property</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>
                    for more information.</p>
                <p>The <code>page-progression-direction</code> attribute also allows the content
                    flow direction to be globally specified for all Content Documents to facilitate
                    rendering (see the <span class="phrase"><a
                            href="epub30-publications.xhtml#attrdef-spine-page-progression-direction"
                            >page-progression-direction</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0"
                    >[<abbr>Publications30</abbr>]</a></span>).</p>
            </section>
            <section class="section" title="3.2 Content Documents" id="sec-gls-content-docs">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-gls-content-docs">›</a> </span>3.2 Content
                    Documents</h3>
                <p>XHTML Content Documents leverage the new HTML5 directionality features to improve
                    support for bidirectional content rendering: the <code>bdi</code> element allows
                    an instance of directional text to be isolated from the surrounding content, the
                        <code>bdo</code> element allows directionality to be overridden for its
                    child content and the <code>dir</code> attribute allows the directionality of
                    any element to be explicitly set.</p>
                <p>XHTML Content Documents also support ruby annotations for pronunciation support
                    (which makes them supported in Navigation Document links, as well).</p>
                <p>SVG Content Documents support the rendering of bidirectional text, but do not
                    include support for ruby.</p>
            </section>
            <section class="section" title="3.3 CSS" id="sec-gls-css">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-gls-css">›</a> </span>3.3 CSS</h3>
                <p>EPUB 3's support for new CSS3 modules enables typography for many different
                    languages and cultures. Some specific enhancements include:</p>
                <div class="itemizedlist"><ul class="itemizedlist">
                        <li class="listitem"><p>support for vertical writing, which also provides
                                Reading Systems the ability to allow users to toggle
                            direction;</p></li>
                        <li class="listitem"><p>better handling of emphasis, such as the inclusion
                                of bōten;</p></li>
                        <li class="listitem"><p>better control over line breaking, so that breaks
                                can occur at the character level for languages that do not use
                                spaces to delimit new words; and</p></li>
                        <li class="listitem"><p>better control over hyphenation, to further
                                facilitate line breaking.</p></li>
                    </ul></div>
            </section>
            <section class="section" title="3.4 Fonts" id="sec-gls-fonts">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-gls-fonts">›</a> </span>3.4 Fonts</h3>
                <p>EPUB 3 does not require that Reading Systems come with any particular set of
                    built-in system fonts. As occurs in Web contexts, Users in a particular locale
                    may have installed fonts that omit characters required for other locales, and
                    Reading Systems may utilize intrinsic fonts or font engines that do not utilize
                    operating system installed fonts. As a result, the text content of a Publication
                    might not natively render as intended on all Reading Systems.</p>
                <p>To address this problem, EPUB 3 supports the embedding of fonts to facilitate the
                    rendering of text content, and this practice is recommended in order to ensure
                    content is rendered as intended.</p>
                <p>Support for embedded fonts also ensures that Publication-specific characters and
                    glyphs can be embedded for proper display.</p>
            </section>
            <section class="section" title="3.5 Text-to-speech" id="sec-gls-tts">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-gls-tts">›</a> </span>3.5
                    Text-to-speech</h3>
                <p>EPUB 3's support for PLS documents and SSML attributes increases the
                    pronunciation control that Authors have over the rendering of any natural
                    language in text-to-speech-enabled Reading Systems. Refer to <a class="xref"
                        href="#sec-tts" title="2.10 Text-to-speech">Text-to-speech</a> in the
                    Features section for more information on these capabilities.</p>
                <p>The combination of CSS Speech and inline SSML phonemes also allows fine control
                    over ruby.</p>
            </section>
            <section class="section" title="3.6 Container" id="sec-gls-container">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-gls-container">›</a> </span>3.6
                    Container</h3>
                <p>The OCF container format supports UTF-8, allowing for internationalized file and
                    directory naming of content resources.</p>
            </section>
        </section>
        <section class="chapter" title="4 Accessibility" id="sec-accessibility">
            <h2 class="title"><span class="link-marker"><a class="hidden-reveal" title="Link here"
                        href="#sec-accessibility">›</a> </span>4 Accessibility</h2>
            <p>A major goal of EPUB is to facilitate content accessibility, and a variety of
                features in EPUB 3 support this requirement. This section reviews these features,
                detailing some established best practices for ensuring that EPUB Publications are
                accessible where applicable.</p>
            <p>It is important to note that while accessibility is important in its own right,
                accessible content is also more valuable content: an accessible Publication will be
                adaptable to more devices and be easier to reuse, in whole or in part, via human and
                automated workflows. The EPUB Working Group strongly recommends that Authors use
                EPUB tools that generate accessible content.</p>
            <section class="section" title="4.1 Navigation" id="sec-access-nav">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-access-nav">›</a> </span>4.1
                    Navigation</h3>
                <p>EPUB 3 improves on NCX documents with the addition of <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-content-document-epub-nav"
                        title="EPUB Navigation Document">EPUB Navigation Document</a>s. As noted in
                        <a class="xref" href="#sec-content-docs" title="2.5 Content Documents"
                        >Content Documents</a> above, the new features these provide represent a
                    more universal and flexible navigation system.</p>
                <p>The need to navigate a document is not exclusively an accessibility issue, but a
                    complete Navigation Document is key for all Users to be able to easily and fully
                    access the contents of a document. The primary <span class="property">toc</span>
                    <code>nav</code> element (as defined in <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-xhtml-nav-def-types-toc">The toc nav
                            Element</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span>) should fully reflect the structure
                    of the Publication, as a result.</p>
                <p>For highly structured documents where it might not be desirable to display the
                    complete table of contents to Users, the display level can be modified using the
                        <a class="biblioref" href="epub30-references.xhtml#refHTML5"
                        title="HTML5: A vocabulary and associated APIs for HTML and XHTML"
                            >[<abbr>HTML5</abbr>]</a>
                    <span class="property">hidden</span> attribute without minimizing the
                    information that is available for accessible Reading Systems.</p>
                <p>Authors are also encouraged to supply additional <code>nav</code> elements if
                    their Publications contain non-structural points of interest, such as figures,
                    tables, etc. in order to further enhance access to the content.</p>
            </section>
            <section class="section" title="4.2 Semantic Markup" id="sec-access-semantic-markup">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-access-semantic-markup">›</a> </span>4.2
                    Semantic Markup</h3>
                <p>HTML5 supports a number of new elements intended to make markup more semantically
                    meaningful (e.g., <code>section</code>, <code>nav</code>, <code>aside</code>)
                    and introduces more clearly defined semantics for some HTML4 elements. These
                    elements, in conjunction with best practices for authoring well-structured Web
                    content, should be utilized when creating EPUB XHTML Content Documents. These
                    additions allow content to be better grouped and defined, both for representing
                    the structure of documents and to facilitate their logical navigation. XHTML
                    Content Documents also natively support the inclusion of ARIA role and state
                    attributes and events, enhancing the ability of Assistive Technologies to
                    interact with the content.</p>
                <p>EPUB 3 further introduces the <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#attrdef-epub-type">epub:type</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> attribute, which is meant to be
                    functionally equivalent to the W3C Role Attribute <a class="biblioref"
                        href="epub30-references.xhtml#refPFRoleAttribute" title="Role Attribute"
                            >[<abbr>Role</abbr>]</a>. This attribute allows any element in an XHTML
                    Content Document to include additional information about its purpose and meaning
                    within the work, using controlled vocabularies and terms. Refer to <span
                        class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-xhtml-semantic-inflection">Semantic
                            Inflection</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> for more information.</p>
            </section>
            <section class="section" title="4.3 Dynamic Layouts" id="sec-access-layout">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-access-layout">›</a> </span>4.3 Dynamic
                    Layouts</h3>
                <p>The design center of EPUB is dynamic layout: content is typically intended to be
                    formatted on the fly rather than being typeset in a paginated manner in advance
                    (i.e., expecting a particular sized "page"). This core capability is useful, for
                    example, for optimizing rendering onto different sized device screens or window
                    sizes, and it facilitates and simplifies content accessibility. </p>
                <p>While it is possible to incorporate more highly formatted content in EPUB — for
                    example via bitmap images or SVG graphics, or even use of CSS explicit
                    positioning and/or table elements to achieve particular visual layouts — Authors
                    are strongly discouraged from utilizing such techniques. They are not reliable
                    in EPUB since many Reading Systems render content in a paginated manner rather
                    than creating a single scrolling <a class="glossterm"
                        href="epub30-terminology.xhtml#gloss-viewport" title="Viewport">Viewport</a>
                    and since each Reading System may define its own pagination algorithm. If these
                    techniques are required to convey the content of the publication (for example,
                    for graphic novels), <span class="phrase"><a
                            href="epub30-publications.xhtml#sec-fallback-processing-flow"
                            >fallbacks</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>
                    should always be included.</p>
                <p>In general, it is preferable to achieve visual richness by using <a
                        class="glossterm" href="epub30-terminology.xhtml#gloss-stylesheet"
                        title="EPUB Style Sheet (or Style Sheet)">EPUB Style Sheet</a>s without
                    absolute sizing or positioning.</p>
            </section>
            <section class="section" title="4.4 Aural Renditions and Media Overlays"
                id="sec-access-overlays">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-access-overlays">›</a> </span>4.4 Aural
                    Renditions and Media Overlays</h3>
                <p>Aural renditions of content are important for accessibility and are a desirable
                    feature for many other Users. A baseline to facilitate aural rendering is to
                    utilize semantic HTML designed for dynamic layout. Refer to <a class="xref"
                        href="#sec-tts" title="2.10 Text-to-speech">Text-to-speech</a> for more
                    information on how to use the native facilities that EPUB XHTML Documents
                    include. </p>
                <p>Media Overlays provide the ability to synchronize the text and audio content of a
                    Publication, a feature already familiar to readers of DAISY Digital Talking
                    Books. Overlays transcend the accessibility domain in their usefulness: the
                    synchronization of text and audio as a tool for learning to read, for example,
                    being of benefit in many circumstances. </p>
            </section>
            <section class="section" title="4.5 Fallbacks" id="sec-access-fallbacks">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-access-fallbacks">›</a> </span>4.5
                    Fallbacks</h3>
                <p>Not all formats are accessible in their native format, and not all Users prefer
                    to read in the default format provided. EPUB defines a variety of means for
                    providing fallbacks so that alternate renditions of a Publication can be made
                    available in these cases.</p>
                <p>Publication and content-level fallbacks are defined in <span class="phrase"><a
                            href="epub30-publications.xhtml#sec-fallback-processing-flow"
                            >Restrictions and Fallbacks</a>
                        <a class="biblioref" href="epub30-references.xhtml#refPublications3"
                            title="EPUB Publications 3.0">[<abbr>Publications30</abbr>]</a></span>.
                    These allow for the alternate rendition of specific resources within a
                    Publication, such as SVG images or video clips.</p>
                <p>In addition, multiple instances of a complete work can be delivered in a single
                    Publication by defining multiple <code>rootfile</code> elements in the OCF
                    container file (as described in <span class="phrase"><a
                            href="epub30-ocf.xhtml#sec-container-metainf-container.xml">Container –
                            META-INF/container.xml</a>
                        <a class="biblioref" href="epub30-references.xhtml#refOCF30"
                            title="Open Container Format 3.0">[<abbr>OCF3</abbr>]</a></span>). This
                    kind of fallback may be used, for example, so that a formatted graphic novel
                    defined via a sequence of SVG pages can be accompanied by an accessible text
                    version defined via XHTML.</p>
            </section>
            <section class="section" title="4.6 Scripting" id="sec-access-scripting">
                <h3 class="title"><span class="link-marker"><a class="hidden-reveal"
                            title="Link here" href="#sec-access-scripting">›</a> </span>4.6
                    Scripting</h3>
                <p>EPUB 3 adopts a progressive enhancement approach for scripted content, whereby
                    scripting must not interfere with the integrity of the document (i.e., must not
                    result in information loss when scripting is not available). Consequently,
                    although documents that do employ scripting <span class="phrase"><a
                            href="epub30-contentdocs.xhtml#sec-scripted-content">may provide
                            fallbacks</a>
                        <a class="biblioref" href="epub30-references.xhtml#refContentDocs3"
                            title="EPUB Content Documents 3.0"
                        >[<abbr>ContentDocs30</abbr>]</a></span> to further facilitate access to
                    their contents, the documents must be accessible without them.</p>
                <p>Several mechanisms in EPUB can further minimize and constrain scripting within
                    Publications to improve accessibility:</p>
                <div class="itemizedlist"><ul class="itemizedlist">
                        <li class="listitem"><p> The declarative <span class="phrase"><a
                                        href="epub30-contentdocs.xhtml#sec-xhtml-epub-trigger"
                                        >trigger element</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> added to the
                                EPUB HTML5 profile enables image or textual elements to act as
                                controls for audio and video playback (for example, to start, stop
                                and pause playback). This element eliminates the common use of
                                scripting to include similar functionality.</p></li>
                        <li class="listitem"><p>The <span class="phrase"><a
                                        href="epub30-publications.xhtml#sec-mediaType-elem"
                                        >mediaType element</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refPublications3"
                                        title="EPUB Publications 3.0"
                                        >[<abbr>Publications30</abbr>]</a></span> provides a means
                                of encapsulating script-based support for rendering custom XML
                                vocabularies or other custom content types, as well as future-proofs
                                Publications in case such content types are natively supported in
                                future Reading Systems.</p></li>
                        <li class="listitem"><p>The semantic inflection capability provided by the
                                    <span class="phrase"><a
                                        href="epub30-contentdocs.xhtml#sec-xhtml-content-type-attribute"
                                        >type attribute</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> enables Authors
                                to provide hints to Reading Systems about content properties. One
                                use case is to define elements such as images and video as having a
                                zoomable property value, in which case a Reading System may provide
                                a means for Users to access an expanded view that is out-of-line
                                with the normal layout. Such rollover effects are typically
                                implemented via scripting in Web contexts, but scripting cannot be
                                readily implemented given the wide variety of layouts that a Reading
                                System may generate.</p></li>
                        <li class="listitem"><p> The <span class="phrase"><a
                                        href="epub30-contentdocs.xhtml#sec-xhtml-epub-switch">switch
                                        element</a>
                                    <a class="biblioref"
                                        href="epub30-references.xhtml#refContentDocs3"
                                        title="EPUB Content Documents 3.0"
                                            >[<abbr>ContentDocs30</abbr>]</a></span> provides a
                                declaractive means for Authors to tailor the content displayed to
                                Users without having to resort to scripted solutions.</p></li>
                    </ul></div>
                <p>Best practices for accessible scripting in Web documents, such as provided in <a
                        class="biblioref" href="epub30-references.xhtml#refARIA"
                        title="Accessible Rich Internet Applications (WAI-ARIA) 1.0"
                            >[<abbr>WAI-ARIA</abbr>]</a>, should always be consulted, and use of
                    scripting should be reserved for situations in which interactivity is critical
                    to the User experience.</p>
            </section>
        </section>
    </body>
</html>
